Cob: a leaderless protocol for parallel Byzantine agreement in incomplete networks

Abstract

In this paper we extend the Multidimensional Byzantine Agreement (MBA) Protocol, a leaderless Byzantine agreement for lists of arbitrary values, into a protocol suitable for wide gossiping networks: Cob. This generalization allows the consensus process to be run by an incomplete network of nodes provided with (non-synchronized) same-speed clocks. Not all nodes are active in every step, so the network size does not hamper the efficiency, as long as the gossiping broadcast delivers the messages to every node in reasonable time. These network assumptions model more closely real-life communication channels, so Cob may be applicable to a variety of practical problems, such as blockchain platforms implementing sharding. Cob has the same Bernoulli-like distribution that upper-bounds the number of steps as the MBA protocol. We prove its correctness and security assuming a supermajority of honest nodes in the network, and compare its performance with Algorand.

Cob: a consensus layer enabling sustainable sharding-based consensus protocols

“…Cob [6] is a novel BFT protocol (i.e. a strong consistency protocol) which is an evolution of the MBA protocol [7].…”

“…Outline In Section 2 we provide a high-level but comprehensive description of Cob, which is fully presented in [6]. In particular we underline the properties that Cob satisfies and the assumptions it relies on.…”

“…In particular we underline the properties that Cob satisfies and the assumptions it relies on. In Section 2.2 we describe its workflow and building blocks, namely the Multidimensional Graded Consensus and Multidimensional Binary Byzantine Agreement [7,6].…”

“…The problem above is discussed in [7,6] by considering the presence of malicious nodes in the network, and this leads to the identification of two properties that such a consensus protocol must satisfy in order to maximise the amount of agreed-upon meaningful data.…”

“…Since it is assumed that the network is complete, it is essential, for sake of efficiency, that the network is composed of a small number of nodes (which does not exceed the hundreds). The evolution of Cob presented in [6] overcomes these shortages, and can be adopted by wide networks of nodes (even with millions of participants), making it way more practical and its adoption suitable for the network of permissionless blockchains. From now on, when we refer to the protocol Cob we refer to the second definition [6], unless explicitly specified.…”